Recently, allergic patients such as patients with atopic dermatitis have been increased. As for foods, proteins contained in egg white, soybean and milk are recognized as the three main allergens. Then, so-called an elimination diet is introduced as a symptomatic treatment. However, of the above allergens, soybean proteins are widely contained in Japanese traditional foods such as soy sauce, miso (fermented soybean paste), tofu (soybean curd), aburaage (fried tofu), koridofu (freeze-dried tofu) and yuba (membrane-like soybean protein food) as well as in other foods which contain soybean proteins as a part of their raw materials. Moreover, recently, variations of foods utilizing functional properties of soybean proteins, such as emulsification, gel-formation, film-formation, water-retention, viscosity, foaming and the like have increased, which makes selection of the elimination diet difficult.
Ogawa et al. (Biosci. Biotech. Biochem., 57:1030 (1993)) have identified a soybean protein component having a high reactivity to IgE antibody from an atopic patient against soybean as Gly m Bd 30k which is a fraction showing a 34 kDa band in SDS-PAGE electrophoresis. In addition, they have also found that 7S fraction contains a large amount of Gly m Bd 30k, while 11S fraction and whey fraction fractionated by the method of Than and Shibasaki (J. Agric. Food Chem., 24:1117-1121(1976)) scarcely contains it.
However, it is very difficult to separate and remove Gly m Bd 30k from 7S fraction by a known method in an industrial scale. On the other hand, even when proteins are collected only from 11S fraction and whey fraction, the sum of them amounts to only 30 to 40% (25 to 30% from 11S fraction alone) of whole soybean milk proteins. Thus, there is a problem that a yield of low-allergenic soybean proteins is low. Moreover, there is a problem of productivity that a delicate pH adjustment of soybean milk and a long-term treatment at a low temperature are needed in fractionation of 7 S fraction and 11 S fraction, or a problem that functional properties of soybean proteins are considerably changed when 7 S protein is absent.
Although, afterwards, Ogawa et. al. have re-named Gly m Bd 30k as "Gly m I", in the present specification, the protein is referred to as "Gly m Bd 30k" or "allergenic protein".